Video coding technique is one of the foundations of multimedia application. Viewing the vigorously developing high-tech industries such as digital TV, new generation mobile communications, broadband communications network, family consumer electronics, the common techniques mostly concentrate on multimedia information processing technique of which the main content is video and audio, especially on the data compressing technique.
High efficient video coding and decoding technique is the key to realize storing and transmitting multimedia data at high quality and low cost. At present, the commonly used encoding and decoding methods include: predictive coding, orthogonal transform coding, vector quantization coding, etc. These methods are all based on the signal processing theory, which is also called 1st generation coding technique; the currently popular international standards about picture coding are all based on this coding technique, which employs the method combined of motion compensation based on block matching discrete cosine transform and quantization. The typical international standardization organizations involved in the above technique, International Standardization Organization/International Electro-technical Commission, No. 1 Joint Technical Group (ISO/IEC JTC1), carried out international standards of MPEG-1, MPEG-2, MPEG-4, etc.; International Telecommunications Union (ITU-T) brought forward H.26x voluntary standard in series. These video coding standards are widely used in the industries.
All the aforesaid video coding standards adopt Hybrid Video Coding policy, usually including four main modules such as predicting, transforming, quantizing, information entropy coding etc.
The predicting module has the main function to predict the current image to be coded by using the coded and reconstructed image(inter prediction); or to predict to predict the current image part (or macro block) to be coded by using the coded and reconstructed image part (or macro block) in images (intra prediction); the transforming module has the main function to transform the input image block into another space so as to converge the energy of inputted signals at transform coefficient of low frequency for lowing relativity within the elements of image block and being useful for compressing; the quantizing module has the main function to map the transformed coefficient to a limited element aggregate helpful for coding; information entropy coding module has the main function to indicate the quantized transform coefficients with variable-length codes according to the statistical discipline. Video decoding system includes similar modules, mainly for reconstructing the decoded image through the procedures of entropy decoding, inverse quantizing, inverse transforming etc the input code streams
Usually, the video coding/decoding system further includes some supplementary coding tools besides the above mentioned modules. These tools will also contribute to the coding performance (compression ratio) of the entire system.
In MPEG-2 system, Group of Picture (GOP) header is used in the front of one Intra Prediction encoding (hereinafter referred to as I Frame), which includes three kinds of identification field: the first identification field, broken_link, indicates whether the B Frame, which is closely behind I Frame, can be correctly reconstructed, for any modification or compile of the coded I Frame will affect the correct reconstruction of B Frame; therefore, it needs GOP header to indicate whether the B Frame, which is closely behind I Frame, can be correctly reconstructed; the second identification field, closed_gop, indicates whether the B Frame, which is closely behind I Frame, only uses the backward reference, and if only the backward reference is used, the B Frame, which is closely behind I Frame, can be reconstructed even if I Frame is modified; the third identification field, time_code, indicates “time and control code of video tape recorder”, but it does not take effect at the decoding end.
The 59 bit identification needs to be introduced into the above three kinds of identification fields. However, the first two identification fields s (broken_link and closed_gop) are the identification fields adopted by the outdated technique, and fundamentally seldom used at present; the third identification field (time_code) is not necessary in most application circumstances, which is only used infrequently; therefore, if these identification fields are coded/decoded, it will affect the coding/decoding efficiency.